The overall objective of this research is to characterize the effects of metabolic, pharmacologic, and mechanical stimuli on the activity of cardiac receptors with nonmyelinated vagal afferents (C-Fiber) and to determine whether these stimuli can significantly alter the inhibition of the vasomotor center by these cardiac receptors. During the current year (1977-78) a laboratory was set up to record C-fiber potentials. In addition a specially constructed pump is nearly completed and will be used to inflate a small balloon positioned in the left atrium or ventricle to mechanically activate these C-fibers in a modified Langendorf preparation. The first study in the coming year (1978-79) will examine the effect of various digitalis preparations on the activity of mechanically activated C-fibers. Preparations of different polarity will be studied since the polarity may effect the extent of binding and thus the relative influence of a given preparation on the receptor. The second study will compare the effects of dl-propranolol, a beta adrenergic blocking agent, with the effect of d-propranolol on the discharge of receptors with nonmyelinated cardiac vagal afferents. The relative influence of the nonspecific membrane stabilizing properties of the d-isomer and the racemic mixture will thus be determined.